It amusing, how long it wasn't noticed, but apparently when you build Samba documentation together with the Samba suite the vfs_zfsacl.8 is not build.
That's no wonder as it's missing from the docs-xml/wscript_build. That possibly wasn't noticed cause pre-packaged manpages are build through other route, via the configure/make, where *.xml globing catches all the pages.
The issue was noticed by Anodos on FreeNAS forum.